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Yamaha CR-820 relay not clicking!

Z

ZanderTibell

New Member
Hey! I have a Yamaha CR-820 that I don’t get any sound from. The unit powers up fine and the lights and everything else seem to work but the amplifier section seems to be blown. No fuses have blown but the relay doesn’t click. The output transistors doesn’t seem to be shorted and all four reads about the same. I have little knowledge in the field, just a happy amateur that wants to learn. I have repaired a amplifier before but this problem seems more subtle. FYI I’m from Sweden so English isn’t my native language. I hope you could help me. I have measured almost all the transistors and drivers in the amplifier section and no one appears to be blown, also (what I believe is) the emitter resistors read fine (the four next to each other) and the resistors with ”socks” on them read fine (I think they are the fusible resistors). The 68 ohm resistors read perfectly. I can’t find the problem. When I measure the output transistors leg to ground I get a high voltage that I don’t know if it’s right. I put my negative lead to the negative speaker output and the positive to each leg and when I measure I get between 16 and 18 volts on the output transistors. On the output transistor casings I get ~43v. On the voltage regulator with the heatsink I measure 44,4 vdc between the heatsink and negative speaker terminal. On the big coils near transistor 722 I get 19 volts on one of them and 24 volts on the other. Between speaker negative and TP1 and TP2 I got 24v. I tried removing the output transistors and measuring them separately and then seem to be good and read about the same.

After leaving it on for about 45 minutes the transistors 719, 720, 721 and 722 get really warm. I know it’s normal but I can’t touch them without burning my fingers.

I have heard that a member called ”Avionic” is an expert on these and I hope I can get in touch with him. I would really appreciate input on this and I would be happy if you could dumb it down and make it like a lesson cause is want to learn more and I think that other people would appreciate a lecture too! Kind regards Zander Tibell
 
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Do you have a dim bulb setup? If yes. Remove all 4 output transistor.. plug amp into dim bulb. Turn it on. See if relay will kick in..
if all 4 transistors have same read from B-E and B-C.. it is blown..need new one.. try that first..
You will need 2 of:

And 2 of:

They are a pair for each channel.. RIGHT CHANNEL: MJ21196G + MJ21195G. LEFT CHANNEL: MJ21196G + MJ21195G.

The original:
2SB557 = MJ21195G
2SD427 = MJ21196G

You will also need mica film.

Get extras transistor and film to have as spare, in case something went wrong and you short out the new output transistors.

First, i would turn down (left, counter clockwise) the Idle trim pot all the way or both channel..
Install the new (4) output transistor..
Power up on Dim bulb, 60w.. A MUST.
Check for dim bulb glow and relay activity..
 
If the outputs are blown something else will be as well most likely up stream.

Instead of the installing the outputs use a 470 ohm 1 watt resistor between the Emitter and Base of the output pads. Then see if you can make any Bias or DC offset adjustments. Otherwise you might just end up blowing the new outputs.

@avionic will have better advice for sure.

Athanasio
 
hej suspect TR712, TR714 or somewhere in that area, Solder joints ok? No burnt tracks?
Plz measure b/c/e to GND (blk spkrs) for both TR712 and TR714
 
Unfortunately I don’t have a dim bulb tester. I tried removing all the output transistors and starting the receiver but still the relay won’t click. I measured about 0,5 on all of them in one direction and OL in the other so I guess they work as they should?

The pads in these boards seems to be very brittle and break easily. I have repaired the pads and all the components are connected as they should. I can try measuring TR712 and TR714 again and see what voltages I get there and I will update you. Kind regards Zander
 
At the relay I have about 15vdc. There’s only voltage on these two legs, nothing at the others. The coil in the relay measures 165ohms.
 

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ZanderTibell said:
On TR714 u get 14v , ~57v and ~57v on the legs/casing. On TR712 I get ~57v, ~63v and ~61v.
Click to expand...
Not really the resolution I need.
Service manual has the following guiding values
TR714
e -43.6V?...... you ~57?
c -1.09 ~14?
b -42.3? ~57?

TR712
e -45.6V ~63?
c -43.6 ~57?
b -44.8 ~61?

Your values are significantly higher, suggest a basic health check of power supply, also check if any mains voltage selector is correctly set.

Wanting to see a 0.6V(abouts) voltage drop between b & e.

ZanderTibell said:
At the relay I have about 15vdc. There’s only voltage on these two legs, nothing at the others. The coil in the relay measures 165ohms.
Click to expand...
The relay should have at least 6 pins, left&right audio in, L&R audio out, relay coil in&out. Maybe 2 additional pins for relay off position. 15V is about the dc offset you previously measured, expect this on the R-audio in pin, expect the other pins to be 0V. Relay coil at 165ohms seems good.
 
I found one problem, the voltage regulator (T806) that I’m gonna switch out today. Just gonna build myself a dimbulb tester first. mbz, what kind of information do you need?
 
That’s awesome you got it figured out. Good thing it was just a simple fixed. The idle current was probably set in correctly and pushing too much power through the output transistors killing it.
 
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